1. Field of the Invention
The present invention relates to a back-illuminated type solid-state image pickup device including a light receiving surface of a photoelectric conversion element provided on a back surface side of a semiconductor chip, and a camera module using the solid-state image pickup device.
2. Description of the Related Art
In recent years, video cameras and electronic cameras have prevailed. CCD or amplifying solid-state image pickup devices are used in these cameras. The amplifying solid-state image pickup device (CMOS image sensor) has an image pickup pixel section composed of a plurality of pixels two-dimensionally arranged on one semiconductor chip, and a peripheral circuit section located outside the image pickup pixel section. Various MOS transistors for transfer, amplification, or the like are provided in the pixels of the image pickup pixel section. Light entering each of the pixels is photoelectrically converted by a photodiode to generate a signal charge. The transfer transistor and the amplifying transistor convert the signal charge into an electrical signal and amplifies the electrical signal to output the signal from the pixel to the peripheral circuit section through a signal line.
In the solid-state image pickup device configured as described above, in order to increase the numerical aperture of the photodiode (the ratio of light incident on the photodiode to light incident on the pixel), each pixel uses a microlens to condense the incident light on the photodiode through between interconnects. However, in this case, the light condensed by the microlens is partly shielded by a signal interconnect from the photodiode. This may pose the following problems.
(1) Since the light is partly shielded by the interconnects, sensitivity decreases.
(2) The light shielded by the interconnects is partly reflected and enters the photodiode of the adjacent pixel, resulting in color mixture.
(3) The layout of the interconnects is limited, and the characteristics of FET are degraded by restrictions such as the hindrance of the placement of the interconnects over the photodiode and the prevention of passage of thick interconnects.
(4) Miniaturization is difficult for a reason similar to that in (3).
(5) Light is likely to obliquely enter pixels in a peripheral area and to increase reflect, and darker shading occurs in areas closer to the periphery.
(6) When an attempt is made to produce a CMOS image sensor using an advanced process with a further increased number of interconnect layers, the distance from the microlens to the photodiode increases, and such difficulties as described above become more serious.
(7) (6) inhibits the use of a library for the advanced CMOS process, and the layout of circuits registered in the library needs to be changed or the interconnect layers are limited, thus increasing the required area. This increases costs and the area of each pixel.
To solve these problems, what is called a back-illuminated type solid-state image pickup device has recently been proposed which includes a light receiving surface of the photodiode provided on a back surface side of the semiconductor chip (see, for example, Jpn. Pat. No. 3722367).
However, with the back-illuminated type solid-state image pickup device, when a tester is used to test how well a wafer has been produced, images cannot be tested at a wafer level. That is, with the normal CMOS image sensor, a color filter and an on-chip microlens are formed on the wafer, and the light receiving surface is irradiated with light. Signals are obtained via a pad formed in the peripheral circuit section to check images. However, with the back-illuminated type, the wafer has no test pad on the back surface side (light receiving surface). Thus, an electrode needs to be provided on a front surface side of the wafer where interconnects are formed. Thus, it is difficult to irradiate the CMOS image sensor with light for image testing at the wafer level. Consequently, the wafer is diced into individual pieces, and a mounting step is then carried out to form camera modules for testing. Thus, manufacturing efficiency decreases.